Optimization of Seawater Reverse Osmosis Desalination Networks with Permeate Split Design Considering Boron Removal

Increasingly strict constraints on the boron concentration for safe drinking and irrigation water present a tremendous challenge for the design of seawater reverse osmosis (RO) desalination systems. This work presents an optimization study of a seawater reverse osmosis RO network with permeate split (PS) design under boron concentration restrictions. Front part permeates with better quality and higher flux are sent directly to the product, and back part permeates are reprocessed in pass 2 with high pH value. The irreversible thermodynamic model is employed to describe the membrane transport behavior of boron. Constraints for the system flow and operation conditions are added to guarantee safe operating of the RO system. Both single-product and two-product RO systems are optimized for different types of feed seawater. Results show that the PS design is mainly dominated by the boron constraints, while the system recovery is mainly controlled by the feed salt concentration. Due to the upper bound of pH for pass 2, PS design could be introduced for pass 2 to improve the boron rejection. For a two-product output system, the permeates from both RO pass 1 and pass 2 could be split and sent to different products. In general, PS design could offer lower water cost, lower energy consumption, and smaller system size compared with normal design. Not only the operation conditions but also the flow structure of the RO system should be adjusted according to both membrane fouling and degradation with time.